QuickOffice comes with a file manager (called FileManager!), which allows you to create folders, move files, etc. Only trouble with it is that it only works on files on the SD drive and cloud storage (e.g. Google Docs). It won't even acknowledge the existence of the Nook's internal storage.

It looks like it will work. I just tried it out using Google Docs, my PC, and the Nook. I uploaded an epub into Google Docs. Then I went into Google Docs on the Nook with FileManager and copied the file into the clipboard (you use the clipboard for file copying). Then I switched over to the books folder on the SD card and did a paste. The epub was there. I then looked in the Library on the Nook and that epub was listed in the books area.

So you could use Calibre the same way (instead of Google docs - I was too lazy to hook up the Nook to my PC).

I am seeing that this could be a pretty nifty way to get files to your Nook without ever connecting the nook to your PC - using Google Docs (or Dropbox, Box, etc), and FileManager.

Edit - also, to further explain, you do not have to use the browser to log into Google Docs on the Nook in order to get files. FileManager can be configured to automatically log into these cloud sites and treat them as a virtual drive on the Nook, so it is seamless. Very nice!